This research will examine the selective appearance of cell surface molecules and their function in embryonic cell recognition. Four new technologies will be brought together to dissect the changes in the embryonic cell surface which account for specific cell recognition events. Cells of the three primary germ layers and the two extracellular membranes of sea urchin embryos have been isolated to permit specific interactions to be studied. A new cell binding assay has been adapted such that the molecular basis for initial recognition events can be studied in isolation without complications arising from subsequent cellular processes. Already observed during the initial binding phase has been Ca++ dependent and a Ca++-independent component, recognition specificity, differential initial strengths, and an ability to relate binding site number with cell-cell dislodgment force. The components of initial binding and subsequent processes will be approached, first by isolating events through experimental manipulation of the binding assay, then by a focused attack on each individual event. An extensive panel of monoclonal antibodies has been screened. A number of the monoclonals have revealed novel patterns of protein expression during early development and three monoclonals appear to identify cell recognition antigens. These studies will be continued. Finally, with the cell surface antigens identified by monoclonals, and with a growing knowledge of intracellular trafficking pathways which direct glycoproteins to the cell surface, the localization of antigens will be studied. Central to this aspect of the work is ligatin, a plasma membrane protein that functions as a cell-surface baseplate for peripheral glycoproteins. The family of glycoproteins associated with ligatin will be studied biologically and biochemically to determine their roles at the cell-surface, especially their possible contribution to adhesive mechanisms. In addition, the recognition between ligatin and the glycoproteins it binds seems to be due a specific oligosaccharide containing phosphate. The structure and synthesis of this carbohydrate will be pursued.